Transformer



April 21, 1942. e. CAMlLLl TRANSFORMER Filed July 28, 1959 a o. as o n a o o o o o o 000 an 0 0 n wait V6 vvvvv UV/VWM/WWHWWHW a HHHHHNNNNAM w UHHMWHwnwwflnm p Glug|ilmo cgmlma, WWI/v76.

His Attorney.

Patented Apr. 21, 1.942

1 UNITED STATES PATENT OFFICE Guglielmo General New York Mass, assignmto Camilli, Pittafield, Electric Company, a corporation of 16 Claims.

My invention relates to transformers and to current transformers and is of particular advantage in connection with a current transformer with its primary winding arranged for connection to a high voltage electrical circuit. I In a high voltage transformer, the insulation usually forms a considerable part of the total volume of the transformer and any rearrangement which will permit a reduction in-the necesand the complete transformer is consequently very. compact and may .be produced very economically.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Fig. 1

is a vertical, sectional view of a transformer enclosed in its casingand constructed in accordance with the invention; Fig. 2 is a sectional view 'of the transformer showing details of construction; Fig. 3 is a sectional view of a portion of a modified form of the transformer; Fig. 4 is a view of a portion of a transformer partly in section showing another modified form; and Fig. 5 is a view of one of the details of the transformer.

Like reference characters indicate similar parts in all the figures of the drawing.

- leads H.

edge of the ring I! and enclosing the terminal The high voltage windingmay be enclosed in the ring or annular shield member I! in any suitable manner. Thus, the ring may comprise a pair of complementary portions. For example, the ring may be slit in a longitudinal plane which, in this case, is the plane of the paper, as indicated by the portion which is shown in full lines in Fig. 2 at the section of the ring l2 which has been partly broken away. In assembling the high voltage winding and the ring, the ring portions may be disposed on either side of the high voltage winding and the tube ll fit over the upper edge or neck of the ring l2, and the winding l0 may be spaced from the inside surface of the ring as shown in Fig. 2, by any suitable means. This ring [2 and tube II form paper wrapped about the hollow ring l2 and the The transformer shown in Figs. 1 and 2 includes a primary or high voltage winding ll provided with a pair of terminal leads II. In a current transformer the primary winding is connected in series with an electrical circuit so that the voltage between the turns of the winding and ,buttheseleads ll andthehighvoltage tube II to the required thickness. The shield I4 is formed with smoothly curved outer surfaces about which the crepe paper may be easily and smoothly wrapped. The radius of curvature of each part of the shield II is sufilcient to prevent corona and the shield has the further function that it prevents corona on the enclosed high voltage coil IO and its leads ll because it surrounds theseparts and is maintained at approximately the same potential. The surface of the insulation It surrounding the hollow ring I! is provided with a closely fitting metal sheath or shield II which is extended a short distance up the sides of the insulation surrounding the tube It, the

upper portion of this shield il being flared outwardly and the extreme edge being smoothly rounded to prevent corona. The insulated high voltage winding ll surrounds one side of a magnetic core it upon which are distributed the insulated turns of a secondary or low voltage winding is, this low voltage winding being connected to low voltage terminals II. The core member may be positioned with respect to the primary winding in any suitable manner. In the embodiment shown in Figs. 1 to 3, inclusive, the core member and secondary winding are assembled after the assembly of the high voltage winding,

ring i2, insulation i6 and sheath H by passing the material forming the core, and the turns comprising the secondary winding through and around the insulated and sheathed annular ring so that the primary and secondary windings will be linked in a' magnetic circuit. When the transformer is assembled according to this procedure, neither the core member nor the secondary winding is present to hinder the operation of insulating and sheathing'the high voltage,winding.

The insulated high voltage winding I is enclosed in a metal casing or shield 2|. The insulated high voltage leads II and tubular shield 3 extend up through an opening in the cover of the casing 2| and are surrounded by a porcelain wall 22 having its upper end closed and sealed by a metal cap 23. The metal casing 2|, the porcelain wall 22 and the cap 23 constitute a complete casing for the transformer. The high voltage leads ii are connected to high voltage terminals 24 extending through the upper end of the casing.

The metal shield or sheath i1 is connected to ground by a strap 25 so that it is at ground potential and-needs no insulation from the casing 2| and so that this casing need be only just large enough to surround the insulated high voltage winding iii. The grounded shield extends up through the opening in the cover of the casing 2| to shield the adjacent edge of the cover from voltage stresses.

The portion of the ground shield i1 surrounding the insulation about the high voltage winding i0 may be provided by wrapping strips of thin conducting material, such as metal about the surface of the insulation, as shown in Fig. 1. In order to avoid a short-circuited turn around the core i8, a gap 28 is left in the grounded shield i! and a gap 21 is provided in thehollow metal ring i2.

A series of electrostatic shields 28 are embedded in the insulation l6 surrounding the high voltage leads H and their tubular shield l3. These electrostatic shields 28 are distributed longitudinally and radially in the insulation to improve the longitudinal and radial distribution of the high voltage throughout this insulation. The necessary thickness of the insulation i6 surrounding the tube i3 will be a minimum if the voltage distribution in the insulation is uniform.

The transformer casing is filled with insulating fluid or liquid, such as a mineral oil, to a level 29 as indicated in Fig. -l, space being left above the liquid to permit thermal expansion and contraction. This insulating liquid fills the high voltage shield I4 and all spaces surrounding the transformer and it also completely impregnates the crepe paper insulation l6. In order to obtain the best results it is of course necessary that the insulation l6 be completely free of all moisture and air or other deleterious gas. A very effective way to remove the moisture is to force a heated gas into the upper open end of the shield l4, an inert gas such as heated and thoroughly, dried carbon dioxide being desirable. The hollow shield l4 and the external grounded shield i! are formed with a number of small openings 30 and the heated compressed gas in the shield I4 is forced slowly through these openings. and through all the pores of the insualtion ii until all the moisture has been removed from the in- .heated gas to escape more easily through this thinner portion of the insulation than through the thicker portion within the ground shield II. The openings iii are therefore closer together or larger or both in the ground shield I1 and in the hollow ring i2 of the shield i4 than in the upper'portion of the tubular shield i3 surrounded by the thinner insulation. This distribution of the openings 30 tends to equalize the flow of the heated gas through all parts of .the insulation at the same time that it is bein forced through the insulation ii to remove moisture. The equalization of the flow of heated gas through the insulation it may also be improved by using a more porous crepe paper in the thick er insulation around the high voltage winding Hi and the lower part of the tubular shield i3 than in the insulation about the upper portion of the tubular shield i3 where the insulation after the drying of the insulation is complete.

This result may be secured by producing a partial vacuum in the inner high voltage shield I4 and maintaining this vacuuni while the insulating liquid is very slowly introduced into the cas-,

ing. It has been found desirable in some cases to maintain the vacuum in the high voltage shield i4 and to introduce the insulating liquid so slowly as to require several days to reach its final level 29.

Since the shield |2 is'at substantially the same potential as the primary winding, the oil which is disposed between the inner shield l2 and the primary winding will be substantially free of electrostatic stress. Thus, if bubbles form in the oil inside the shield 2 as the result of a short circuit, for example, no harm will be done because the bubbles will merely rise to the top of the structure. Furthermore, since the outer shield or sheath i! is at substantially the same potential as the secondary winding or grown,

sulatlon. The insulation I6 is gradually reduced in thickness toward the upper end of the shield l4 so that there would be a tendency for the no insulation is needed outside the sheath ii.

In the modified form of the invention shown in Fig. 3 the construction is similar to that shown in Figs. 1 and 2 except that the electrostatic shields 2,8 are omitted from the insulation Ii. The distribution of the high voltage through the insulation I8 is not so uniform and a greater thickness of the insulation i6 is therefore necessary for the same voltage but this may not be objectionable if the voltage of the high voltage winding l0 and its leads ii is not too high.

In the modified form of the invention indicated in Fig. 4 the magnetic core I. is enclosed within the hollow ring l2 of the inner high voltage shield H, the turns of the high voltage winding l0 being distributed along the core within the ring l2 andthe turns of the loyi voltage winding l9 being distributed around the outer surface of the grounded sheath ii. In order to avoid short-circuited turns in the ring |2' extending around the coreiii, the ring should be provided with a gap, as has already been described above with respect to Fig. 2.. Since the ring is split in order to permit easy'assembly the parts r 2,280,625 explained with respect is m. 2, in order where heat may be more readily dissipated. The a metal tube l3 and the hollow ring I! of the shield it are large enough in cross-section to permit the liquid heated by the high voltage winding II in the ring II to rise by convection through the tube [3 to the upper part-of the casing where it may be cooled. The insulation l6 surrounding the internal shield ll prevents any effective dissipation of heat by conduction from the high voltage .winding II, but this winding I! may be satisfactorily cooled by the convection flow of liquid between the winding 12 and the liquid in the upper end of the transformer casing.

The invention has been explained by describing and illustrating a particular high voltage current transformer and certain modified forms thereof, but it will be apparent that changes may be made without departing from the spirit of the invention and the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

, 1. A current transformer including a high voltage winding, insulation around said winding, a grounded metal sheath enclosing and closely fitting said insulation, a casing enclosing said windi ing and its insulation and sheath, said casing having an opening, and terminal leads extending through said opening from the winding, said insulation and sheath extending around said leads and through said opening.

2. A current transformer including a high voltage winding, insulation around said winding, a

grounded metal sheath enclosing said insulation, a casing enclosing saidwinding and its insulation and sheath, said casing having an opening, terminal leads extending through said opening from the winding, said insulation and sheath extending around said leads and through said opening, and electrostatic shields distributed radially and longitudinally in said insulation to improve the voltage distribution therein and decrease the age winding, terminal leads connected to the winding, a hollow metal shield surrounding said winding and leads, insulation surrounding said shield, a casing enclosing. the transformer, and insulating liquid in said. casing and shield, the shield providing communication between the perforations to permit gas in the shield to be forced through the insulation to remove moisture.

6. A current transformer including a high voltage winding, terminal leads connected to the winding, a hollow metal shield surrounding said winding and leads, and porous insulation surrounding said shield, said metal shield-having perforations to permit gas in the shield to be forced through the. insulation to remove moisture, the perforations being arranged to permit the gas to reach the insulation around the winding more easily than that around the terminal leads.

'l. A transformer including a high voltage winding enclosed in a conductive shield terminating in a conducting tube, terminal leads connected to the winding and extending through said tube, means connecting said winding and said shield whereby said shield is at substantially the potential of said winding, insulation around said shield including said tube, and a grounded metal sheath enclosing said insulation and extending part way along said tube.

8. A transformer including a high voltage winding, a conducting member substantially surrounding said winding, said conducting member being'spaced from said winding, an insulating liquid disposed in the space between said wind-.

ing and said conducting member and surrounding said high voltage winding, and means electrically connecting said conducting member to said winding so that said liquid will be substantially free of electrostatic stress.

9. A transformer including a high voltage. winding, solid porous insulation surrounding said winding, conducting shielding members contiguous with .the inside and outside surfaces of said insulation, said inside shield being adjacent said high voltage winding and being electrically connected therewith, said outside shield being connected to ground, and an insulating liquid. surrounding said transformer, said shields being perforated so that said liquid may permeate said insulation and surround said winding.

10. A transformer including a high voltage winding, spaced-apart conducting shields surrounding said winding, solid porous insulation within the space between said shields, said inner shield being adjacent 'to and electrically connected to said high voltage winding, said outer shield being connected to ground, and an insulating liquid surrounding said transformer, said shields being perforated so that said liquid may (ill permeate said insulation and surround said winding.

l1. A transformer including a high voltage winding, solid porous insulation surrounding said winding, a conducting sheath surrounding said insulation, an insulating liquid, said transformer being immersed in said liquid, said sheath being perforated so. that said liquid may permeate said insulation and conductive .meansspacing said insulation from said winding so as to provide a space around said high voltage winding in which said insulating liquid may circulate.

winding space in the shield and, the upper por- Q tion of the casing to permit cooling of the winding by convection currents in the liquid.

5. A current transformer including a high volt-- winding and leads. and porous insulation surrounding'said shield, said metal shield living 12. A. transformer including an annular high voltage winding, solid porous insulation surrounding said winding, a conducting sheath surrounding said insulation, an insulating liquid, said transformer being immersed in said liquid, said sheath being perforated so that said liquid may permeate said insulation, an annular core member, and a low voltage winding having turns distributed around said core member, said core member and low voltage winding passing through and around said sheath, said sheath bein grounded so that failure of said insulation will not cause damage to said low voltage winding.

13. A transformer including an annular core member, a primary winding distributed along said core member, insulating means surrounding said annular core member and winding, a grounded conducting sheath enclosing said insulation, and a secondary winding distributed around said sheath.

14. A transformer including a hollow annular insulating means, a core member, a primary winding distributed along said core member, said core member and primary winding being within said hollow part of said insulating means, conductive means around said primary winding and within said insulating means, and a secondary winding distributed around and adJacent the outside surface of said insulatingmeans.

15, A transformer including a high voltage voltage winding, solid porous insulation surround ing said winding, conducting shielding members contiguous with the inside and outside surfaces of said insulation, said inside shield being adjacent said high voltage winding and also being electrically connected therewith, said outside shield being connected to ground, and an insulating liquid surrounding said transformer, said inside shield being perforated so that said liquid. may permeate said insulation and surround said leads connected to said winding and extending through said tube, solid porous insulation surrounding said shield and tube, a grounded sheath enclosing said insulation and extending part way along said tube, a low voltage winding linking said primary winding adlacent said grounded sheath, and an insulating fluid surrounding said 5 transformer, said shield and sheath being perforated so that said fluid may permeate said insulation and surround said winding.

- r GUGLIE'IMO CAMILLI. 

